ok i wrote it like you said and now its work properly, amazing ! i found the other problem, my creature had a random mouvement in his update() methode and of course its override the arrive() methode.
I can manage that problem myself i think 
jb4x thank you again, i was afraid i cant manage this issue for the end of the week but now i can move forward !
i gonna update my github when i make my changes.
A BIG thank you again.